It is well known that an antenna is the key element to transmit/receive (transceive) microwaves in wireless technology such as wireless communication and wireless data transfer, where the antenna transforms electrical currents generated by a transmitter into microwaves and transmits the microwaves in free space. The antenna also captures microwaves and transforms them into electrical currents, which are then processed by a receiver.
Further, electromagnetic pulse, which is generated by the presence of electric currents in an antenna, radiates in to free space from the site of an antenna by the speed of light, and the direction of which the electric field travels is perpendicular to the direction of the travel of the electromagnetic pulse. The electric field is related to only two parameters, and they are the distance and the radiation angle. The intensity of the electric field decreases with the square of the distance from the antenna, and the graphical representation of the intensity of the radiation of the electric field to the radiation angle from the perpendicular is defined as a radiation pattern.
Please refer to FIG. 1 that shows an established radiation pattern of a typical omni-directional antenna in conventional use. As shown in the figure, the electric field of an omni-directional antenna A in a horizontal plane H that is perpendicular to the antenna A is denoted as a radiation pattern P, and the radiation pattern P is the largest in intensity of all radiation patterns of the antenna A (in comparison with radiation patterns lying in planes not perpendicular to the antenna A). Besides, due to the omni-directional characteristic of the antenna A, the radiation pattern P is of approximately equal intensity in every direction (i.e. radiation angle) in the horizontal plane H.
FIG. 2, a view of a radiation pattern of another typical omni-directional antenna of conventional use, shows the radiation pattern P1 of an omni-directional antenna A1 in the horizontal plane H that is perpendicular to the antenna Al. It is obvious that the intensity of every position with the established radiation pattern P1 in the horizontal plane H is of approximate equivalence.
On the other hand, wireless technology such as peer-to-peer connection and satellite communications are best fit with antennas that concentrate their electric field to a rather small region. Since such antennas are of focused radiation, their overall power of the energy output is able to decrease to a desired level, while the energy density per unit area is able to increase to a certain amount. The radiation of such antennas in other directions, therefore, is relatively weak in intensity and small in coverage-the physical geological area where signal is still at a level that can be transceived-and that reduces the occasions of meaningless electromagnetic interferences. Such antennas are the so-called directional antennas.
FIG. 3 is a view of an established radiation pattern of a typical directional antenna of conventional use, and a radiation pattern P2 of a directional antenna A2 in the horizontal plane H that is perpendicular to the antenna A2 is shown in the figure. Apparently, the intensity of radiation at any position within the radiation pattern P2 in the horizontal plane H exists no equivalence.
Further, omni-directional antennas of the electronic devices in conventional use are those of dipole antennas, Marconi antennas, etc., while directional antennas of the same use are those of flat antennas, microstripe antenna, disk antenna, and PIFA antennas. In addition, once the kind of antenna used in an electronic device is determined in advance, the omni-directional or the directional characteristic of the electronic device with the specific kind of the antenna arranged therein is determined.
Although an electronic device with an omni-directional antenna is noted with the homogeneity of the radiation pattern the antenna generates, the distance of the wireless signal transceiving of the omni-directional antenna is relatively shorter than that of a directional antenna of the same power in a desired direction, while the gain, which is the relative increase in radiation at the maximum point expressed as a value in dB above a standard, is smaller than that of a directional antenna in the direction of focused radiation pattern. However, an electronic device with a directional antenna, on the contrary, is strongly limited by the direction when it comes to the transceiving of wireless signals.